JPH0969821A - Stereo receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce noise low in noise density without causing incompatibility to listeners. SOLUTION: The frequency of received signal is discriminated, and the audio signals of the left and right channels are separated based on selectivity and respectively outputted as sound. When no noise is generated, the selectivity is controlled in accordance with the voltage corresponding to the electric field intensity of received signal outputted from an S meter circuit 32 through a selectivity control circuit 34. When the noise component of received signal is extracted by a multipath detection circuit 42, the noise component is integrated by 1st and 2nd integration circuits 47 and 48. When the noise density is low and only the 1st integration circuit 47 reaches an ON voltage, in accordance with the voltage level set in another terminal p2 of a diode D6 of the circuit 34, the selectivity is reduced to about 10dB. When the noise density is high and both circuits 47 and 48 reach the ON voltage, in accordance with the voltage level set in another terminal p4 of a diode D7 of the circuit 34, the selectivity is reduced to almost <=4dB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stereo receiver for receiving frequency modulation stereo broadcasting and the like.

[0002]

2. Description of the Related Art In frequency modulation (hereinafter abbreviated as "FM") stereo broadcasting and the like, multipath noise, which is noise that is suddenly generated during reception of the broadcasting, may be mixed. Multipath noise is a direct wave that reaches the receiving antenna directly from the transmitting antenna and a reflected wave that reaches the receiving antenna when the electric wave emitted from the transmitting antenna is reflected by an object and passes through multiple transmission paths with different lengths. It is noise generated when the transmitted signal is received by the receiving antenna at the same time.

As a method of reducing multipath noise,
There is a method to reduce the degree of stereo broadcast channel separation when multipath occurs. The degree of channel separation is the degree to which the signal of the left or right channel leaks and is mixed with the signal of the right or left channel when transmitting a stereo broadcast. The lower the degree of separation, the lower the noise level of the sound demodulated and reproduced from the transmitted signal.
The reproduced sound is heard by the listener as a sound close to a monaural sound.

In order to reduce noise such as multipath noise that is suddenly generated, it is necessary to reduce the degree of separation at the same time when noise is generated. Also, the lower the degree of separation,
To the listener, the sound is heard as monaural sound. In this way, to provide a good stereo broadcast to the listener,
After the noise disappears, it is necessary to immediately increase the degree of separation and return to stereo broadcasting.

If the degree of separation is reduced every time multipath noise occurs intermittently, the listener will hear the sound of the reproduced voice, the localization, and the left and right speaker outputs so as to change intermittently. To be done. Therefore, each time, a feeling of sound fluctuation is felt, and the stereo sound is heard as if switched to monaural sound. Therefore, an uncomfortable feeling occurs when listening to the stereo broadcast.

As described above, in order to reduce the change in the reproduced voice, a method is considered in which the degree of separation is lowered only when multipath noise with high frequency occurs. 17 to 19 are graphs showing the relationship between the occurrence timing of multipath noise and the change in the separation degree when the method of reducing the separation degree is used only when high-frequency multipath noise occurs.

The separation control means used in such a method has, for example, an integrating circuit, and when multipath noise is generated, the capacitor of the integrating circuit is charged according to the number of times the noise is generated. When the multipath noise ceases, the capacitor begins to discharge. The separation degree control means controls so as to reduce the separation degree when the output from the integrating circuit is equal to or higher than a predetermined level.

When the noise density, that is, the number of times noise is generated in a unit time is small, as shown in FIG. 17 (1), the next multipath noise is generated once after the discharge of the capacitor of the integrating circuit is completed. Has occurred in. When such intermittent noise is mixed, FIG. 17 (2)
As indicated by the solid line 1 of No. 3, the degree of separation is not reduced and the maximum value Max is always maintained.

Further, when the noise density is medium, as shown in FIG.
As shown in (1), for example, after the noise is generated a few times, the generation of the noise is once stopped and the capacitor is discharged. Occurs. At this time, FIG. 18 (2)
As indicated by the solid line 2 in FIG. 2, the generation of noise is repeated a plurality of times a plurality of times, and the degree of separation is reduced from time t1 when the capacitor is sufficiently charged. At this time, the degree of separation is reduced to a value S1 that is a value close to 0 dB. When the generation of noise is finished 2-3 times, it takes time from time t2 to time t3,
The degree of separation gradually returns to the maximum value Max.

Further, when the noise density is high, FIG.
As shown in (1), a lot of noise is continuously generated in a short time. At this time, as indicated by the solid line 3 in FIG. 19 (2), the capacitor of the integrating circuit is sufficiently charged immediately after noise is generated, and the degree of separation is reduced from time t4. When the generation of many noises ends, the degree of separation lowered from time t5 to time t6 is gradually restored to the maximum value Max.

[0011]

As described above, if the separability is reduced only when a large number of noises are continuously generated, that is, only when multipath noise having a high noise density is generated, it is possible to generate a sporadic event. Noise that occurs in
It becomes difficult to reduce multipath noise that occurs at a noise density that does not reach a predetermined density value such as three times. Further, as shown in FIGS. 18 (1) and 18 (2), in the case of reducing the multipath noise generated at a noise density equal to or lower than a predetermined density value, the separation is lowered after the noise is generated. Attack time, which is the time until
9 (1) and FIG. 19 (2) are longer than in the case where many noises are continuously generated.

Further, when reducing the multipath noise, the degree of separation is reduced to near 0 dB. When returning the lowered degree of separation to the original maximum state Max, the degree of separation is gradually increased and gradually returned.
This is to prevent the listener from feeling that the sound is suddenly switched from the monaural sound to the stereo sound by abruptly changing the degree of separation.

As shown in FIGS. 18 (1) and 18 (2), when the noise density is medium, for example, from the time t1 during which the degree of separation is reduced to reduce noise. The release time for returning the state in which the degree of separation is lowered to the maximum state, as compared with the time up to time t2,
That is, the time from time t2 to time t3 becomes long.
Therefore, the time for restoring the resolution is longer than the time for which the resolution should be lowered in order to reduce noise. Therefore, the time for which the degree of separation is reduced becomes longer than the time for reducing noise.

An object of the present invention is to provide a stereo receiver capable of reducing multipath noise promptly without causing the listener to feel discomfort from the reproduced voice when listening to a broadcast. is there.

[0015]

The present invention is based on a receiving means for receiving a received signal, a demodulating means for demodulating the received signal in response to an output of the receiving means, and an output of the demodulating means based on a separation control signal. And a channel separation means for separating and deriving the demodulated received signal into audio signals for each of the left and right channels at the separation degree corresponding to the level of the separation degree control signal, and receiving in response to the output of the receiving means. An electric field strength detecting means for detecting the electric field strength of the signal and outputting a separation degree control signal for controlling the channel separating means so as to decrease the separation degree as the electric field strength becomes smaller; A noise extraction means for extracting a noise signal from the noise extraction means, a noise density measurement means for measuring the noise density in response to the output of the noise extraction means, and a response for the output of the noise density measurement means. Separation rate control means for outputting a separation degree control signal for controlling the channel separation means so as to set the separation degree small, or continuously, and electric field strength detection means when noise is not extracted by the noise extraction means. And a switching means for applying the separation control signal outputted from the channel separation means to the channel separation means and, when noise is extracted, supplying the separation control signal output from the separation control means to the channel separation means. It is a stereo receiver. According to the present invention, the stereo receiver demodulates the broadcast wave of the FM stereo broadcast received by the receiving means by the demodulating means, separates the audio signal for each of the left and right channels from the demodulated received signal, and outputs the stereo broadcast. To play. The audio signal for each of the left and right channels is separated in the channel separating means provided in the subsequent stage of the demodulating means by calculating the demodulated received signal based on a separation control signal described later. The separation control signal is output based on the strength of the electric field strength of the received signal or the presence or absence of noise superposition of the received signal. The separation control signal based on the electric field strength is from the electric field strength detection means,
It is generated and output based on the electric field strength detected by the detection means. The separation degree control signal is a signal for controlling the channel separation means so that the separation degree decreases as the electric field strength decreases. The noise superimposed on the received signal is extracted from the received signal by the noise extraction means.
The cause of noise includes multipath interference. Multipath noise caused by multipath interference is
It is noise that occurs suddenly and momentarily reduces the electric field strength of the received signal. In a stereo receiver that receives and demodulates stereo broadcasting, as a method of reducing sudden noise such as multipath noise from the reproduced sound, the degree of separation that separates the left and right audio signals from the received signal is reduced. There is a method to make it. Reducing the resolution is
This is equivalent to bringing stereo sound with different sound signals in the left and right channels close to monaural sound in which the same sound signal is output from the left and right channels. When the noise is extracted by the noise extracting means, the noise density measuring means measures the number of multipath noises generated within a predetermined time, that is, the noise density. The separability control means generates a separability control signal based on the noise density. The separability control signal based on the noise density is a signal in which the separability is set smaller as the noise density is higher. In stereo broadcasting, the sum signal obtained by adding the left and right channel audio signals and the difference signal obtained by subtracting the left and right channel audio signals are obtained.
They are included in the low frequency side and high frequency side of the modulation frequency of the received signal, respectively. In the channel separation circuit, in obtaining the left and right channel audio signals from the sum signal and the difference signal, the noise that is likely to be included in the high frequency side of the modulation frequency is reduced as the ratio of the level of the difference signal to the sum signal is reduced. be able to. Since multipath noise and the like are likely to be included particularly in the high frequency side, it is possible to reduce the multipath noise by lowering the degree of separation. The isolation control signal based on the electric field strength and the isolation control signal based on the noise density are
Either one of the signals is applied to the channel separation means by the switching means depending on the presence or absence of noise. When noise is not extracted by the noise extraction means, the separation degree control signal based on the electric field strength is given to the channel separation means, and the separation degree changes in accordance with the change in the electric field strength of the received signal. When noise is extracted, a separation degree control signal based on the noise density is given to the channel separation means, and the larger the noise density, the smaller the separation degree is set. by this,
When noise is extracted, the separation of the left and right channels can be reduced to reduce the reproduced noise. Moreover, the degree of separation at the time of noise extraction can be set according to the noise density.

According to the present invention, the channel separating means is
When a noise signal is extracted and the noise density is equal to or higher than a predetermined density, the degree of separation is set to be less than a predetermined value,
When a noise signal is extracted and the noise density is less than a predetermined density, the isolation is set to about 10 dB, and the predetermined value is set to a value that can sufficiently reduce noise. Characterize. According to the invention, the channel separation means reduces the separation degree in a plurality of steps when the separation degree control signal based on the noise density is given. When the noise density is equal to or higher than the predetermined density, the degree of separation is set to a value that can sufficiently reduce the noise. When the noise density is less than the predetermined density, the degree of separation is set to about 10 dB. The lower the degree of separation of the channels of the stereo broadcast, the more noise can be reduced from the reproduced sound. Further, as the channels are separated, the audio signals of the opposite channel are mixed with the audio signals of the left and right channels, and the reproduced sound comes closer to monaural sound. Therefore, when noise is generated, particularly when the noise density is large and a large number of noises are generated in a short time, it is preferable to reduce the degree of separation to a value that can sufficiently reduce the noise. Such a separation value is
For example, the value is 4 dB or less. The sound reproduced by separating the sound signal with the degree of separation reduced to 4 dB or less is close to monaural sound. The sound image, localization, and left and right speaker output sound pressures differ between monaural sound and stereo sound. Therefore, if the degree of separation is reduced to a predetermined value of, for example, 4 dB or less each time noise is generated, the listener feels that stereo sound and monaural sound are frequently switched, which causes a feeling of strangeness. When the noise density is lower than the predetermined density, the noise is generated intermittently or only for a short time, so that the degree of separation is about 10%.
The noise is sufficiently reduced only by reducing it to dB.
When the separation is reduced to about 10 dB, the listener
It is difficult to perceive that the stereo sound approaches the monaural sound, and you do not feel a significant change in the stereo feeling that you feel when you are listening to the stereo sound. Therefore, only when the noise density is high and a lot of noise is generated, the degree of separation is set to be less than a predetermined value, and the stereo sound is made as close as possible to the monaural sound to reduce the noise. When the noise density is low, the degree of separation is reduced to a level at which the noise is sufficiently reduced and a stereo feeling can be maintained, and the left and right channel audio signals are separated. This ensures that whenever noise is generated,
It is possible to prevent the stereo sound from frequently approaching the monaural sound, and causing the listener to feel a sense of distorted sound.

Further, according to the present invention, the separation degree control means controls the channel separation means so as to reduce the separation degree, and when the noise signal is no longer extracted from the received signal, the separation degree is increased with time. It is characterized in that the time change rate of the degree of separation, which is controlled so as to be returned to the original state and increases with the passage of time, is set smaller as the noise density becomes smaller. According to the present invention, the separability control means gradually increases the separability with the passage of time when noise no longer occurs after noise is generated and lowers the separability, and the separability before noise is generated. Return to. The rate of change over time that increases the degree of separation is
It is determined according to the noise density. As described above, if the degree of separation is reduced in order to reduce noise, the stereo voice approaches a monaural voice having a different sound image or localization.
When the degree of separation is once lowered and the reproduced sound is brought close to monaural sound, the degree of separation is returned to the value before noise generation.
When the degree of separation is suddenly returned from a low level, the listener feels a sense of sway in the reproduced voice due to the sound image or localization difference. When noise is generated, the degree of separation is reduced to a value determined based on the noise density of the generated noise. For example, if the noise density is less than the predetermined density,
The resolution is reduced to about 10 dB. At this time, the listener does not feel the change in the stereo sound due to the decrease in the degree of separation. Therefore, even if the degree of separation lowered to about 10 dB is suddenly returned to the degree of separation before the occurrence of noise, the listener hardly feels the sound fluttering. by this,
The release time, which is the time from when noise is no longer extracted until the reduced resolution is restored to the original resolution, can be shortened according to the noise density. Therefore, when the noise density is low, the release time becomes longer than the time for reducing the noise, and it is possible to prevent that the stereo sound cannot be provided during that time.

In the present invention, the temporal change rate of the degree of separation is such that when the noise density is equal to or higher than the predetermined density,
The release time required for returning the degree of separation set below the predetermined value to the degree of separation determined corresponding to the electric field strength of the received signal is set to be about 1 second or more. To do. According to the present invention, when the noise density is equal to or higher than the predetermined density and the separation degree is set to a low value capable of sufficiently reducing the noise, the release time for returning the separation degree is about 1 second. Set the rate of change of the separation degree with time. As described above, when the separation degree is set to a low value capable of sufficiently reducing noise, for example, 4 dB or less, the listener feels that the reproduced sound is close to monaural sound. Therefore, in such a case, it is necessary to gradually increase the degree of separation so that it is not felt that the stereo sound is suddenly switched to the monaural sound. At this time, the release time is set to 1 second or longer when it is assumed that the next noise is not detected after the noise is no longer extracted until the separation degree before the noise extraction is restored. If the time change rate for increasing the degree of separation is determined so that the release time satisfying such a condition is obtained, it is possible to reduce as much as possible the fluttering sound sensation that a monophonic voice is switched to a stereo voice.

According to the present invention, the noise density measuring means is
A plurality of integrating circuits having mutually different integration time constants for charging or discharging the noise from the noise extracting means, and a plurality of level discriminators that individually discriminate the level of the integrated output of each integrator circuit and have the same discriminating level. Circuit, the separation degree control means responds to the output of each level discrimination means, and when the output of the level discrimination means corresponding to the integrating circuit having a large integration time constant is obtained, the separation degree It is characterized in that the channel separation means is controlled so as to be smaller than when the output of the level discrimination means corresponding to the integration circuit having a small constant is obtained. According to the present invention, the noise density measuring means includes a plurality of integrating circuits and a level discriminating circuit.
Each integrating circuit integrates the noise signal output from the noise extracting means and outputs an integrated output corresponding to the integration result. The level discriminating circuit individually discriminates the integrated output of each integrator circuit, and supplies the discriminating degree control circuit with an output for judging whether or not the integrated output has reached the discriminating level. The integration time constants for charging or discharging noise in each integration circuit are different from each other. The discrimination level of each level discrimination means is equal regardless of the integration time constant of the corresponding integrating circuit. In this way, since the integration time constant of each integrator circuit is different, when the same noise signal is applied to each integrator circuit, the circuit with a larger integral time constant has a larger integrated output level than the circuit with a smaller integral time constant. The rate of increase is small. Therefore, the time from the occurrence of noise until the integral output reaches the predetermined discrimination level becomes longer as the integral time constant becomes larger. Therefore, when a large amount of noise is extracted within a unit time or noise with a short generation interval is extracted, the integrated output sequentially reaches a discrimination level from a circuit having a small integral time constant. That is, as the noise density of the given noise signal is higher, the integrated output of the integrating circuit having a larger integration time constant reaches the discrimination level. Therefore, when the output of the integrator circuit having a large integration time constant reaches the discrimination level, the separability control means reduces the separability as compared with the case where the integrated output of the integrator circuit having a small integration time constant reaches the discrimination level. To control the channel separation means. As a result, the noise density can be measured by a circuit having a simple configuration using a plurality of integrating circuits and level discriminating means. Moreover, since the level discriminating means have the same discriminating level, they can be configured by using circuits having the same configuration.

The present invention is also characterized in that the discharge or charge time constant of each of the integrating circuits in the absence of noise is selected to be larger as the charge or discharge time constant when noise is extracted. According to the invention, the mutual relation of the time constants of the plurality of integrating circuits is equal in the case where noise does not exist and the case where noise is extracted. In the case of an integrating circuit charged by noise, if the charging time constant is larger than other integrating circuits, the discharging time constant is also larger than other integrating circuits. For example, when the integrator circuit is charged by noise, the output from each integrator circuit reaches a desired discrimination level in order from a circuit having a smaller time constant when a noise signal is applied. Circuits with smaller constants decrease below the discrimination level. That is, when the noise density is small, only the integrated output from the integrating circuit having a small time constant reaches the discrimination level, and when noise is no longer extracted, the integrated output immediately drops below the discrimination level. Also, when the noise density is high, the integrated output of the circuit with the smallest time constant and the circuit with the largest time constant reaches the discrimination level, and when noise is no longer extracted, the integrated output discriminates slower than when the noise density is small. Falls below the level.

According to the present invention, the noise density measuring means is
An integrating circuit that has the same integral time constant for charging or discharging noise from the noise extracting means, and a plurality of level discriminating circuits that individually discriminate the level of the integrated output of the integrator circuit and have discriminating levels different from each other. The separation degree control means is responsive to the output of each level discrimination means, and when the output of the level discrimination means having a large discrimination level is obtained, the separation degree is obtained by the output of the level discrimination means having a small discrimination level. It is characterized in that the channel separating means is controlled so as to be smaller than that when it is turned on. According to the present invention, the noise density measuring means includes an integrating circuit for integrating the noise signal and a plurality of level discriminating means for discriminating the level of the integrated output of the integrating circuit. When there are a plurality of integrating circuits, the integrating time constants of the integrating circuits have the same value. Further, the discrimination levels of the level discrimination circuit are different from each other. For example, when the integration time constant of the integrator circuit is a charging time constant for charging noise, if a noise signal is given to the integrator circuit, the noise output becomes shorter when the noise generation interval is shorter and when the noise generation number is larger. To increase. That is, the larger the noise density, the larger the integrated output. Therefore, when the integrated output of the integrating circuit is level discriminated by a plurality of level discriminating circuits having different discriminating levels, the output from the level discriminating circuit having a larger discriminating level is obtained as the noise density of the noise signal is higher. Further, since the integrated output of the integrating circuit increases with the passage of time, the output from the level discriminating circuit is sequentially given to the separation degree control circuit from a circuit having a small discriminating level. Therefore, when the output from the integrating circuit reaches the discrimination level, the separation degree control means controls the channel separation means so that the separation degree decreases as the discrimination level increases. As a result, the noise density can be measured by a circuit having a simple structure using the integrating circuit and the level discriminating means.
Moreover, since the integrating circuits have the same time constant, the output of a single integrating circuit may be determined by the level discriminating means.
It is also possible to use a plurality of integrating circuits having the same configuration.

Further, in the present invention, each level discriminating means is
Responsive to the output of the integrating circuit, when it is above the discrimination level, it outputs a signal of one level, and when it is less than the discrimination level, it has a switching means for outputting a signal of the other level, the separation control means, When a signal of one level is obtained from each level discriminating means, the degree of separation is calculated from among the level discriminating means outputting the signal of one level.
It is characterized in that the channel separating means is controlled so that the discrimination level or the integration time constant of the corresponding integrating circuit becomes a value corresponding to the level discriminating means. According to the present invention, each level discriminating means has a switching means for outputting either one of the one level signal and the other level signal. The switching means outputs a signal of one level when the integrated output of the integrating circuit that charges or discharges noise is equal to or higher than each discrimination level, and outputs a signal of the other level when it is less than the discrimination level. That is, the signal of one level indicates that the noise density is equal to or higher than the predetermined density. A signal at the other level indicates that the noise density is less than the predetermined density. The isolation control means and the switching means obtain information on the noise density of the received signal from the one-level signal or the other-level signal output from each switching means. The magnitude of the noise density is determined according to either the magnitude of the integration time constant of the integrating circuit or the magnitude of the discrimination level of the level discrimination means. Further, the higher the noise density, the later the output timing from the level discrimination means becomes. When the signal of one level is given from the switching means of the plurality of level discriminating means, the separability controlling means sets the separability in accordance with the highest density among the noise densities determined by each level discriminating means. That is, if the measuring means have the same discrimination level, the degree of separation is set according to the output from the level discriminating means corresponding to the circuit having a large integration time constant. If the measuring means have the same integral time constant, the degree of separation is set according to the output from the level discriminating means having a large discriminating level. As a result, when noise occurs, the degree of separation is calculated from the value corresponding to the case where the noise density is small,
When the value is large, the value gradually decreases to the corresponding value. Therefore, for example, when the noise density is measured using a plurality of integrating circuits having different time constants, the attack time, which is the time from the noise generation to the reduction of the separation degree, is always defined by the circuit having the smallest time constant. When the noise generation ends, the output of the integrating circuit decreases faster as the noise density decreases. As a result, a circuit having a higher noise density to be determined continues to give a signal of one level to the separation degree control means for a longer time. Therefore, the degree of separation after the end of noise generation is controlled by the level discriminating means that outputs a signal of one level.
In this way, the degree-of-separation control means can be controlled according to the outputs from the plurality of level discriminating means which respectively judge the value of the noise density.

[0023]

1 is a block diagram showing an electrical configuration of a stereo receiver 11 according to an embodiment of the present invention.

In the tuning circuit 13, the received signal received by the antenna 12 is emphasized only in the signal component near the frequency of the desired wave to be received, further amplified by the high frequency amplifier circuit 14, and then input to the mixing circuit 15. To be done. A local oscillation circuit 16 is provided in association with the mixing circuit 15. The local oscillation circuit 16 is realized by a voltage controlled oscillator or the like, and outputs a local oscillation signal having a frequency corresponding to the tuning voltage from a phase lock loop (hereinafter abbreviated as “PLL”) circuit 17.

The PLL circuit 7 comprises a frequency divider, a reference signal source, a comparator, and a filter. The frequency divider is a control circuit 1 that is demonstrated by a microcomputer or the like.
The local oscillation signal is frequency-divided by a frequency division ratio N corresponding to the frequency of the electrical symbol wave input from the signal line 8. The reference signal source generates a reference signal having a predetermined reference frequency. In the PLL circuit 7, the phase of the reference signal and the frequency-divided local oscillation signal is compared by a comparator to generate an error output. The generated error output is smoothed to a DC voltage by a filter and used as a tuning voltage for the local oscillation circuit 6 and the tuning circuit 3.
Given to. Therefore, when changing the reception frequency, the control circuit 18 changes the value of the frequency division ratio N so that the phase difference between the signal obtained by dividing the local oscillation signal by the frequency division ratio N and the reference signal becomes zero. The tuning voltage changes. This enables stable reception of the desired wave.

The mixing circuit 15 mixes the oscillation signal obtained as described above with the reception signal to obtain an intermediate frequency signal. The obtained intermediate frequency signal is supplied to the intermediate frequency amplifier circuit 20 through the narrow band filter 19 capable of filtering only the frequency component containing the audio signal. The filtering bandwidth of the narrow band filter 19 is selected to be about 180 kHz when receiving FM broadcasting, for example.

The intermediate frequency signal amplified by the intermediate frequency amplifying circuit 20 is applied to the frequency discriminating circuit 21 to perform frequency discrimination and demodulate an audio signal. The demodulated audio signal is stereo-separated by the channel separation circuit 22 into audio signals for each of the left and right channels in accordance with the degree of separation that will be described later, and then provided to the tone control circuit 23.

The tone control circuit 23 comprises, for example, a low-pass filter, an adder, and two multipliers for each channel. In the tone control circuit 23, it is possible to arbitrarily adjust the ratio of the component of the input audio signal through the low pass filter and the component through the bypass line. Increasing the component through the low-pass filter is equivalent to attenuating the high frequency component of the audio signal. The output from the tone control circuit 23 is amplified by the amplifier circuit 24 and then given to the speaker 25 and output as sound.

The output from the intermediate frequency amplifier circuit 20 is given to the S meter circuit 32 via the line 31. The S meter circuit 32 outputs a voltage corresponding to the received electric field strength of the received signal received by the antenna 12. This output voltage is called the S meter voltage. The electric field strength of the received signal may be obtained by AM (amplitude modulation) detection of the output from the intermediate frequency amplifier circuit 20.

The output of the S meter circuit 32 is given to the separation degree control circuit 34 via a line 33 which is a conductor. The resistor R1 is interposed in the line 33. Further, a capacitor C is provided between the ground line and the line portion 35 divided by the resistance R1 of the line 33 and the isolation control circuit 34.
1 is interposed. The resistor R1 and the capacitor C1 are
The time constant circuit 36 is configured. The time constant circuit 36 is provided to prevent the separation degree control circuit 34 from operating in response to a momentary minute movement of the output of the S meter circuit 32. The time constant τ1 of the time constant circuit 36 is set to be larger than the time of instantaneous fluctuation of the output of the S meter circuit 32.

FIG. 2 is a circuit diagram showing a specific configuration of the S meter circuit 32. The output signal 37 from the intermediate frequency amplifier circuit 20 shown in FIG. 3 is given to the S meter circuit 32. The output signal 37 is obtained by superimposing the noise signal 37b on a part of the signal waveform 37a obtained by frequency-converting the received signal. This output signal is given to the diode D1 via the line 31. The output from the diode D1 is given to the amplifier circuit 39 via the line 38. A capacitor C2 is interposed between the line 38 and the ground line. The output signal given from the intermediate frequency amplifier circuit 20 is
It is smoothed in a circuit composed of a diode D1 and a capacitor C2, amplified to a predetermined level in an amplifier circuit 39, and then given to a base terminal of a transistor T1. A voltage of a predetermined level + B is applied to the collector terminal of the transistor T1 from a battery (not shown). At the emitter terminal of the transistor T1,
The lines 33 and 41 are connected. Also line 33,
A resistor R2 is interposed between 41 and the ground line.

The S meter circuit 32 is the intermediate frequency amplifier circuit 2
The signal of the S meter voltage corresponding to the electric field strength of the output signal given from 0 is derived to the lines 33 and 41. FIG.
6 is a diagram showing the relationship between the electric field strength of the output signal given from the intermediate frequency amplifier circuit 20 and the S meter voltage outputted from the S meter circuit 32. FIG. The electric field strength of the output signal from the intermediate frequency amplification circuit 20 and the S of the output from the S meter circuit 32
The meter voltage is proportional as shown by the solid line 40.

The output from the S meter circuit 32 is applied to the multipath detection circuit 42 via the line 41, in addition to the time constant circuit 36. The multipath detection circuit 42 detects a noise component received by being superimposed on the reception signal received by the antenna 12.

FIG. 5 is a circuit diagram showing a specific structure of the multipath detecting means 42. Line 41 is capacitor C
3 is connected to one terminal. The other terminal of the capacitor C3 is connected to one terminals of the resistors R3 and R4 and the transistor T2.
Connected to the base terminal of. The other terminal of the resistor R3 is connected to a battery and a predetermined voltage B + is applied. The other terminal of the resistor R4 is grounded.

A predetermined voltage VC is applied to the collector terminal of the transistor T2 via the resistor R5.
The emitter terminal of the transistor T2 is grounded via the resistor R6. One terminal of the capacitor C4 is connected to the emitter terminal of the transistor T2 and one terminal of the resistor R4. The other terminal of the capacitor C4 is connected to one terminal of the diode D5 on the forward input side and the diode D3.
Is connected to one terminal on the forward output side. The other terminal on the forward input side of the transistor D3 is grounded. The other terminal on the forward output side of the transistor T2 is
It is connected to the lines 45 and 46.

In the multipath detecting circuit 42, first, in the filter composed of the capacitor C3 and the resistor R4, S
The low frequency component of the output from the meter circuit 32 is removed. Then, the output from which the low frequency component is removed is set to resistors R3 to R5,
The output signal is amplified and rectified in the amplifying rectifying circuit including the transistor T2 and the capacitor C4 to extract the noise signal. Finally, full-wave rectification is performed in the full-wave rectification circuit including the diodes D2 and D3 and output to the first and second integration circuits 45 and 46.

Transistor T of multipath detection circuit 42
2 is set so that the noise included in the output signal output from the S meter circuit 32 can be extracted even if the noise is of a small level. That is, the transistor T2 is set to easily saturate even a small level of noise. Therefore, the noise signal output from the multipath detection circuit 42 is a signal indicating only the presence or absence of noise, and the magnitude of the noise, that is, the magnitude of the electric field strength of the received signal is ignored. In this way, the multipath detection circuit 42
Extracts only the noise component from the received signal.

The multipath noise is also generated by the frequency discriminating circuit 2
The output signal from 1 may be filtered by a filter to remove low frequency components, amplified and rectified, and then detected and detected so as to extract noise components. For example, when an FM broadcast receiver or the like is provided with a noise cancel circuit that removes a noise component that is superimposed on a demodulated audio signal, a filter and an amplification rectification circuit that are included in the circuit to detect noise, It may also be used as a circuit for detecting multipath noise.

The output from the multipath detection circuit 42 is sent to the first and second integration circuits 47, 47 via lines 45, 46.
Given to 48. FIG. 6 is a circuit diagram showing a specific configuration of the integrating circuits 47 and 48 and the waveform shaping transistors T3 and T4. In the first integrating circuit 47, the resistors R7 and R8 are connected in series to the line 45. A capacitor C6 is interposed between the line 51 connecting the resistors R7 and R8 in series and the ground line. The other terminal of the resistor R8 opposite to the one terminal connected to the resistor R7 is connected to the base terminal of the waveform shaping transistor T3. A resistor R9 is interposed between the line 52 connecting the resistor R8 and the base terminal of the transistor T3 and the ground line.

The second integrating circuit 48 has a structure similar to that of the first integrating circuit 47. Line 46 has resistors R11,12
Are connected in series via line 54. A capacitor C1 is interposed between the line 54 and the ground line. Further, the one terminal of the resistor R12 on the side connected to the resistor R11 and the other terminal on the opposite side are connected to the base terminal of the transistor T4 for waveform shaping via the line 55. Line 5
A resistor R13 is interposed between 5 and the ground line.

The resistor R7 and the capacitor C6 of the first integrating circuit 47 constitute a time constant circuit 57 having a charging time constant τ2. The resistor R11 and the capacitor C8 of the second integration circuit 47 constitute a time constant circuit 58 having a charging time constant τ3. The resistors R8 and R9 of the first integrating circuit 47 and the second
The resistors R12 and R13 of the integrating circuit 48 are resistors for adjusting the discharge time constants of the integrating circuits 47 and 48, respectively.

The charging time constants of the time constant circuits 57 and 58 are obtained by multiplying the resistance value of the resistor and the capacitance of the capacitor, respectively. Hereinafter, the resistance value of the resistor Rn (n is an integer) is represented as “rn”. The capacitance of the capacitor Cn (n is an integer) is represented by "cn". The time constants τ2 and τ3 are represented by the following equations.

Τ2 = r7 · c6 (1) τ3 = r11 · c8 (2) The time constant τ2 of the time constant circuit 57 is set larger than the time constant τ3 of the time constant circuit 58.

Τ2> τ3 (3) Further, the discharge time constants τ2a and τ3a of the integrating circuits 47 and 48 are also given.
Is represented by the following formula.

Τ2a = (r8 + r9) · c6 (4) τ3a = (r12 + r13) · c8 (5) The discharge time constant τ2a of the first integrating circuit 47 is the second integrating circuit 4
8 is larger than the discharge time constant τ3a. The charging time constants τ2 and τ3 are larger than the discharging time constants τ2a and τ3a. For example, in the first integrating circuit 47, the charging time constant τ2 is set to 3 msec and the discharging time constant is 0.3 m.
sec.

At the base terminals of the waveform shaping capacitors T3 and T4, the first and second integrating circuits 4 are respectively provided.
The outputs from 7,48 are provided. That is, in the first and second integrating circuits 47 and 48, when the capacitor C6 is charged by the pulsed noise signal provided from the multipath detecting circuit 42 and is charged to a predetermined voltage level, the transistors T3 and T4 are turned on. Is turned on,
A current flows from the emitter terminals of the transistors T3 and T4 to the collector terminals. The emitter terminals of the transistors T3 and T4 are grounded. Transistor T3
The collector terminals of T4 are respectively connected to the isolation control circuit 34
Is connected to give the output from the transistors T3 and T4.

Referring again to FIG. Separation control circuit 34
Is composed of resistors R15 to R18, diodes D6 and D7, and a capacitor C10. S meter circuit 3
2 and the resistor R15 are connected via a line 33, a time constant circuit 36 and a line portion 35. Resistors R15 to R1
8 are sequentially connected in series.

A diode D is provided between the resistors R15 and R16.
One terminal p2 of the forward input side of 6 is interposed and connected. A capacitor C10 is interposed between the other terminal p1 on the forward output side of the diode D6 and the ground line. Further, the collector terminal of the transistor T3 described above is connected via a line 61 to the connecting portion between the other terminal p1 on the forward output side of the diode D6 and the capacitor C10.

A diode D is provided between the resistors R16 and R17.
One terminal p4 of the forward input side 7 is interposed and connected. The other terminal p3 on the forward output side of the diode D7
Is connected to the emitter terminal of the transistor T4 described above via the line 62. Resistor R17 resistor R16
A line 63 is connected to the other terminal opposite to the one terminal connected to the diode D7. Line 6
As will be described later, 3 generates a control voltage from the S meter voltage output from the separation control circuit 34, and supplies it to the coefficient multiplication circuit in the channel separation means 22. A resistor R18 is interposed between the line 63 and the ground line.

FIG. 7 is a block diagram showing a specific structure of the channel separation circuit 22. The channel separation circuit 22 is
From the received signal demodulated in the frequency discrimination circuit 21,
Separate the audio signals for each of the left and right channels. The degree of separation indicates the degree to which the generated signal of the left or right channel leaks to the right or left channel and is mixed into the generated signal of the right or left channel. The degree of separation is expressed by the following equation.

[0051]

[Equation 1]

"R" and "L" represent the audio signals of the right channel and the left channel, respectively. "ΔR", "ΔL"
Indicates a right channel audio signal leaked to the left channel and a left channel audio signal leaked to the right channel, respectively.

The channel separating circuit 22 is a sum signal (L + R) formed by adding the audio signals of the right channel and the left channel from the frequency discriminating circuit 21 via the line 66.
Is given. Also, from the frequency discriminating circuit 21 to the line 6
The difference signal (L-
R) is given.

The sum signal (L + R) is applied to the adder 69 after being multiplied by the coefficient k1 in the coefficient multiplication circuit 68. The sum signal (L + R) is given to the subtractor 71 via the line 70.

The difference signal (LR) is applied to the subtractor 71 after being multiplied by the coefficient k1 in the coefficient multiplication circuit 72. The difference signal (LR) is also provided to adder 69 via line 73.

The coefficient multiplication circuits 68 and 72 are connected to and controlled by the separation degree control circuit 34 via a line 63.
The coefficient multiplying circuits 68 and 72 determine the value of the coefficient k1 according to the control voltage from the separation degree control circuit 34, and multiply the difference signal and the sum signal.

In the adder 69, the sum signal [k1 (L + R)] multiplied by the coefficient k1 and the difference signal (LR) are added, and the output is added via the line 74 to the tone control circuit 2
Given to 3. The subtractor 71 subtracts the difference signal [k1 (L−R)] obtained by multiplying the sum signal (L + R) by the coefficient k1, and the output thereof is supplied via the line 75 to the tone control circuit 2
Given to 3. That is, the tone control circuit 23 is supplied with the following signals via the lines 74 and 75, respectively.

(K1 + 1) L + (k1-1) R (4) (k1-1) L + (k1 + 1) R (5) “R” and “L” represent the audio signals of the right channel and the left channel, respectively. . The coefficient k1 is a value determined in proportion to the control voltage given from the separation degree control circuit 34 via the line 63, and corresponds to the separation degree. FIG.
[Fig. 3] is a graph showing the relationship between the coefficient k1 and the control voltage.
As indicated by the solid line 77, the coefficient k1 increases in proportion to the control voltage while the control voltage is 0 to V0. When the control voltage becomes equal to or higher than the predetermined voltage V0, the coefficient k1 is maintained at 1. The coefficient k1 takes any value between 0 and 1.

That is, when the coefficient k1 is 1,
Only the left and right channel audio signals are output from the lines 74 and 75, respectively. When the coefficient k1 is 0, a signal obtained by subtracting the right channel audio signal from the left channel audio signal and a signal obtained by subtracting the left channel audio signal from the right channel audio signal are output from lines 74 and 75. . When the coefficient k1 is a value of 0 or more and less than 1, a signal in a state in which the right channel and left channel audio signals are mixed in the left channel and the right channel in proportion to the coefficient is output according to the coefficient.

With the above circuit configuration, when the multipath noise is not generated, the S meter circuit 3
The coefficient multiplying circuits 68 and 72 of the channel separation circuit 22 are controlled based on the output from 2. When multipath noise is generated, the coefficient value of the coefficient multiplication circuit is controlled based on the number of multipath noise generated within a predetermined time, that is, the noise density.

FIG. 9 is a waveform diagram showing the output of each circuit from the multipath detection circuit 42 to the separation control circuit 34. A solid line 81 in FIG. 9A is a noise signal output from the multipath detection circuit 42. The noise signal is a pulse signal indicating the presence or absence of a noise component.

When the multipath detecting circuit 42 detects that noise is superimposed on the received signal, it switches the level of the noise signal from low level to high level.

FIG. 9B shows the first and second integration circuits 4
The levels of the output signals from 7, 48 are shown. The solid line 83 is
The level of the output signal from the first integrating circuit 47 is shown. A two-dot chain line 84 shows the level of the output signal from the second integrating circuit 48.

The first and second integrating circuits 47 and 48 start charging at the time when noise is detected in the multipath detecting circuit 42, that is, the rising time t11 of the first pulse of the noise signal of FIG. 9 (1). To do. At the time when noise is no longer detected by the multipath detection circuit 42, that is, at the rising time t12 of the last pulse of the noise signal in FIG. 9A, the charging is completed and the discharge is started.

The charging time constant τ3 of the second integrating circuit 48 is smaller than the charging time constant τ2 of the first integrating circuit 47. Therefore, the level of the output signal of the second integration circuit 48 is faster than the level of the output signal of the first integration circuit 47, and the time t13
The on-voltage V1 that is determined in advance is reached. The discharge time constant τ3a of the second integrating circuit 48 is smaller than the discharge value constant τ2a of the first integrating circuit 47. Therefore, at time t12, when the capacitors C6 and C8 of the integrating circuits 47 and 48 start discharging, the level of the output from the second integrating circuit 48 becomes
The voltage drops below the on-voltage V1 earlier than the level of the output from the first integrating circuit 47.

Therefore, the output from the second integrating circuit 48 is the ON voltage V1 from the time t13 to the time t14.
Keep higher level than. The output from the first integrating circuit 47 is the on-voltage V1 during the period from time t15 to time t16.
Keep above the level.

Times t14 and t16 at which the levels of the outputs from the integrating circuits 47 and 48 are switched from the level equal to or higher than the ON voltage V1 to the level equal to or lower than the ON voltage V1 are later than the time t12 when noise is no longer extracted. And the second integration circuit 4
The on-voltage switching time t14 of FIG.
7 is faster than the time t16 at which the ON voltage V1 is switched and is almost equal to the time t12 when noise is no longer extracted.

When the outputs from the first and second integrating circuits 47 and 48 have a level equal to or higher than the ON voltage V1, the transistors T3 and T4 are switched from the OFF state in which no current is passed to the ON state in which a current is passed.

FIGS. 9 (3) and 9 (4) are waveform charts showing switching timings of the off state and the on state of the transistors T3 and T4. The solid line 86 in FIG. 9 (3)
Indicates the switching timing of the off state and the on state of the transistor T3. A solid line 87 in FIG. 9 (4) shows the switching timing of the off state and the on state of the transistor T4. 9 (3) and 9 (4),
It is assumed that the transistor is off when the level is low. The transistor is on when the level is high.

The switching between the ON state and the OFF state of the transistors T3 and T4 is performed by the first and second integrating circuits 47 and 48.
It corresponds to the output from. That is, at time t15, when the level of the output from the first integrating circuit 47 switches from less than the on-voltage V1 to on-voltage V1 or more, the transistor T3 switches from the off state to the on state at time t15. The transistor T3 maintains the on state from the time t15 to the time t16. When the level of the output from the first integrating circuit 47 is switched from the on-voltage V1 or more to less than the on-voltage V1 at time t16, the transistor T3 is switched from the on-state to the off-state.

Similarly, at time t13, the second integrating circuit 4
When the output from 8 switches from less than ON voltage V1 to more than ON voltage V1, transistor T4 switches from OFF state to ON state. From time t13 to time t14, the transistor T4 is kept on. When the level of the output from the second integrating circuit 48 switches from the on-voltage V1 or more to less than the on-voltage V1 at time t14, the transistor T4 switches from the on-state to the off-state. That is, the transistor T3 switches from the off state to the on state later than the transistor T4, and switches from the on state to the off state.

When the transistors T3 and T4 are turned on, in the isolation control circuit 34, the diodes D6 and D
A forward current flows through 7. FIG. 9 (5) shows a diode D
6 is a diagram showing voltage levels at a forward output terminal P1 and a forward input terminal P3 of FIG. In addition, FIG.
(6) is one terminal P on the forward output side of the diode D7
FIG. 3 is a waveform diagram showing the voltage levels of 3 and the other terminal P4 on the forward direction input side.

When no noise is detected, the other terminal P
Voltages V3 and V4, which are voltages obtained by dividing the S meter voltage output from the S meter circuit 32 by the resistors R15 to R18, are applied to 2 and P4. Two-dot chain lines 88, 89 in FIGS. 9 (5) and 9 (6) indicate diodes D6, D.
7 shows the voltage levels of one terminals P1 and P3 of the output terminal 7 in the forward direction. Solid lines 91 and 92 in FIGS. 9 (5) and 9 (6)
Indicates the voltage levels of the other terminals P2, P4 on the forward input side of the diodes D6, D7, respectively.

When transistor T3 is turned on, the voltage level of one terminal P1 is lowered to, for example, about 0 V, and diode D6 is switched to an on state in which a current flows. Therefore, the voltage level of the other terminal P2 drops to the voltage V5 determined by the forward voltage of the diode D6.

When the transistor T3 is switched from the ON state to the OFF state, the voltage level of the one terminal P1 tends to return to the level in the state where noise is not superimposed. At this time, the capacitor C10 connected to the terminal P1 starts discharging. Therefore, the voltage level of the one terminal P1 gradually increases with the discharging of the capacitor C10 from the time t16 when the transistor T3 is switched from the on state to the off state, and returns to the original voltage level at the time t17. To do.

The voltage level of the other terminal P2 of the diode D6 changes almost without delay with respect to the change of the voltage level of the one terminal P1. Therefore, the voltage level of the other terminal P2 is forcibly lowered from the voltage level of the signal output from the S meter circuit 32 to the predetermined voltage level V5 at time t15. When the transistor T3 is turned off at the time t16, that is, when it is determined that the first integration circuit 47 no longer extracts noise, the voltage level of the other terminal P2 gradually increases with time.

When the transistor T4 is switched to the ON state, the voltage level of the one terminal P3 of the diode D7 drops to almost 0 V with almost no delay. On the other hand, when the voltage level of the terminal P3 drops to near 0V, the diode D7
Current will flow into the. Therefore diode D7
The voltage level of the other terminal P4 is regulated by being forcibly reduced to the voltage V5 determined by the forward voltage of the diode D7. When the transistor T4 switches from the ON state to the OFF state, the voltage level of the terminal P3 returns to the original voltage level. As a result, no forward current flows through the diode D7, and the voltage level of the other terminal P4 immediately returns to the level V4 defined by the signal output from the S meter circuit 32.

As described above, the resistors R15 and R1 of the isolation control circuit 34 are controlled by the output from the first integrating circuit 47.
The voltage level of the other terminal P2, which is a point between the two terminals, is controlled. Similarly, the voltage level of the other terminal P4 of the diode D7, which is a point between the resistors R16 and R17, is
It is controlled by the output from the second integrating circuit 48. Thus, in the isolation control circuit 34, the diode D
The voltage levels of the other terminals P2 and P4 of 6, 6 are controlled at timings according to the time constants of the first and second integrating circuits 47 and 48.

As a result, the control voltage applied to the coefficient multiplication circuits 68 and 72 of the channel separation circuit 22 is controlled according to the presence or absence of multipath noise and the number of occurrences of multipath noise within a predetermined time, that is, the noise density.

When multipath noise is not detected, the output from the multipath detection circuit 42 always maintains a low level. Therefore, the outputs from the first and second integrating circuits 47 and 48 do not reach the on-voltage V1, and the transistors T3 and T3
T4 remains off. Therefore, the diodes D6 and D7
The voltage levels at the other terminals P2 and P4 of the other terminals keep the level regulated by the output from the S meter circuit 32. Therefore, the voltage level V11 of the output from the S meter circuit 32 is
Is divided by the resistors R15 to R18, converted into a control voltage of the voltage level V12a, and given to the coefficient multiplication circuits 68 and 72 of the channel separation circuit 22 via the line 63.

[0081]

[Equation 2]

Therefore, in the channel separation circuit 22,
When the sensitivity of the received signal is high corresponding to the electric field strength of the received signal, that is, when the voltage level V11 of the output from the S meter circuit 32 is high, the separation degree is set to the maximum separation degree determined by the channel separation circuit 22. . When the sensitivity of the received signal decreases, the voltage level V11 of the output from the S meter circuit 32 decreases, and the channel separation circuit 22 decreases the degree of separation so as to correspond to the applied control signal.

When multipath noise is generated,
The multipath detection circuit 42 detects only the presence or absence of multipath regardless of the level of multipath noise. When the multipath noise is detected, a pulse signal whose level becomes high when the multipath noise is generated is given to the first integrating circuit 47 and the second integrating circuit 48.

When the noise density of the multipath noise is low, that is, when the number of multipath noises within a predetermined time period is small or the intervals of the multipath noises are wide, the second integrating circuit 48 The output level reaches the ON voltage V1, and the output level of the first integrating circuit 47 does not reach the ON voltage V1.

For example, in FIG. 9 (2) described above,
It is assumed that the multipath noise is generated from time t11 to time t21 and the multipath noise is not generated from time t21 to time t12. At this time, the time constant τ2 of the first integrating circuit 47 is larger than the time constant τ3 of the second integrating circuit 48. Therefore, the output from the first integrating circuit 47 does not reach the ON voltage V1, and only the level of the output of the second integrating circuit 48 reaches the ON voltage V1. Therefore, the transistor T3 remains off and the transistor T4 is switched on.

As a result, a current flows through the diode D6 in the isolation control circuit 34, while the voltage level at the terminal P2 is defined by the output voltage output from the S meter circuit 32. Further, since the transistor T4 is switched to the ON state, the voltage level of the one terminal P3 of the diode D7 drops to near 0V, and a forward current flows through the diode D7. Therefore, the other terminal P4 of the diode D7
The voltage level of is maintained at the voltage level V5 defined by the forward voltage of the diode D7 regardless of the output from the S meter circuit 32. Therefore, the separation control circuit 3
The control voltage V12b output from No. 4 is represented by the following equation.

[0087]

(Equation 3)

The control voltage V12b is applied to the channel separation circuit 2
In No. 2, the maximum separation degree Max when the sensitivity of the received signal is good is determined so that the separation degree decreases to about 10 dB. Resistance values r17, r of the resistors R17, R18
18 is defined so that the voltage V5 defined by the forward voltage of the diode D7 is converted into a control voltage that can be controlled in the channel separation circuit 22 so that the isolation degree is 10 dB.

When the time t12 elapses and the multipath noise no longer occurs, the transistor T4 is switched from the on state to the off state, and no forward current flows through the diode D7. As a result, the voltage level of the other terminal P4 immediately returns to the state defined by the S meter voltage of the signal output from the S meter circuit 32.

Therefore, as shown in FIG. 10 (1), multipath noise is generated at intervals with a single interval, or as shown in FIG.
1 (1), when the noise density is such that multipath noise occurs several times within the time W11, FIG.
As shown in (2) and FIG. 11 (2), when noise occurs, the degree of separation immediately decreases from the maximum value Max to about 10 dB. When noise is no longer detected, the value immediately returns from about 10 dB to the maximum value Max.

Therefore, the attack time, which is the time from the time t11 when the noise signal is detected from the received signal until the separation degree starts to decrease, is the time until the output level of the second integrating circuit 48 reaches the ON voltage V1. Stipulated.
That is, the larger the time constant of the second integrating circuit 48, the shorter the attack time.

When the separation degree is reduced from the maximum value Max to 10 dB, the listener listening to the reproduced stereo broadcast from the stereo receiver 11 hears the sound of the channel on the opposite side to the left and right channels of the stereo broadcast. Signal is mixed,
Since there is no significant change in stereo feeling that is close to that of monaural broadcasting, there is no sound fluctuation. For sporadic multipath noise and multipath noise with low noise density,
If the degree of separation is reduced to about 10 dB, noise can be sufficiently reduced.

Therefore, in the case where a sporadic multipath noise or a multipath noise having a low noise density occurs, the degree of separation is reduced to about 10 dB, and when the noise disappears, the degree of separation is restored almost instantaneously and the degree of separation is lowered. The time spent can be shortened. Therefore, while reducing the multipath noise without causing the listener to feel the sound fluctuation,
It is possible to extend the time for providing stereo broadcasting.
The case where the noise density is low is a case where the density is such that multipath noise is generated several times in a few milliseconds.

When the noise density of the multipath noise is high,
From the multipath detection circuit 42, a noise signal obtained by detecting noise a plurality of times between time t11 and time t12 as shown in FIG. 9A is given to the first and second integration circuits 47 and 48.

The second integrator circuit 48 reaches the on-voltage V1 at time t13, the transistor T4 is turned on at time t13, a forward current flows through the diode D7, and the voltage level of the other terminal P4 reaches a predetermined level V5. Stipulated. Therefore, the control voltage V12b is applied to the channel separation circuit 22 regardless of the voltage level of the output from the S meter circuit 32.

When the output from the first integrating circuit 47 reaches the on-voltage V1 at time t15, the transistor T3 is turned on and a forward current flows through the diode D6.
On the other hand, the voltage level of the terminal P2 is regulated to a predetermined voltage level V5. At this time, the voltage level of the other terminal P4 of the diode D7 is the other terminal B of the diode D6.
2 is defined as a level lower than the voltage level. Therefore, the control voltage V12c applied to the channel separation circuit 22 at this time is defined by the following equation.

[0097]

(Equation 4)

The control voltage V12c is applied to the channel separation circuit 2
2 has a magnitude of voltage for controlling the degree of separation to be, for example, 4 dB or less. By lowering the isolation to 4 dB or less, the ability to reduce noise by controlling the isolation in the channel isolation circuit is maximized. Further, if the degree of separation is reduced to 4 dB or less, the listener does not feel that the sound is separated into the left and right channels. Therefore, when the degree of separation is reduced to 4 dB or less, when the degree of separation is returned to the original maximum value Max, it is felt as if the stereo broadcast and the monaural broadcast are switched, and the sound fluctuation occurs. Therefore, in this case, the degree of separation is gradually increased over time.

After the time t12, when no noise is detected, the first and second integrating circuits 47 and 48 are operated at the time t12.
To start discharging. First and second integrating circuits 47, 4
Regarding the discharge time constant of No. 8, the discharge time constant of the first integration circuit is larger than the discharge time constant of the second integration circuit 48, and the discharge proceeds slowly. Therefore, when the discharge is started from the time t12, the output from the second integrating circuit 48 reaches the on-voltage V1 earlier. Therefore, the transistor T4 switches from the on state to the off state earlier than the transistor T3.

When the transistor T4 is switched from the on state to the off state, the transistor T3 is still kept in the on state. Therefore, the control voltage applied to the channel separation circuit 22 is defined by the voltage level of the other terminal P2 of the diode D6 regardless of whether or not the forward current flows through the diode D7. Therefore, the recovery operation of the separation degree is defined by the discharge time constant of the first integrating circuit 47, the electrostatic capacitance c10 of the capacitor C10, and the like.

The level of the output of the first integrating circuit 47 is at time t.
When the on-voltage V1 or less is reached at 16, the transistor T3 switches from the on-state to the off-state. When the transistor T16 is turned off, the voltage level of the one terminal P1 on the forward output side of the diode T6 becomes
It is defined by the discharge of capacitor C10. Therefore, the release time W15, which is the time from the time t12 when noise is no longer detected to the time t18 when the voltage level returns to the level V3 defined by the output from the S meter circuit 32, is the release time when the noise density is low. Extremely long compared to W16. When the noise density is high, the release time W15 is set to 1 second or longer, for example, 2 seconds.

As a result of the above operation, FIG.
When a large number of multipath noises are detected during the predetermined time W18 as shown in Fig. 12, the separation degree is reduced from the maximum value Max to 10dB immediately after the noises are detected as shown in Fig. 12 (2). It Next, at time t15, the second
When the output of the integrating circuit 47 reaches the ON voltage V1, the degree of separation is further reduced to 4 dB or less. When noise is no longer detected at time t12, the degree of separation becomes
It gradually increases at a time change rate controlled by the discharge of 10 and returns to the maximum separation degree Max when a predetermined release time W15 has elapsed. When the noise density is high in this way, the degree of separation is reduced to near 0 dB, and when noise is no longer detected, the degree of separation gradually returns to the original degree of separation with the lapse of time. The time W18 is, for example, several hundred milliseconds, and when many multipath noises are detected in several hundred milliseconds, it is determined that the noise density is high.

As described above, the stereo receiver 1 of the present embodiment
1, the degree of separation is controlled according to three states: when multipath noise is not detected, when multipath noise is detected and noise density is low, and when multipath noise is detected and noise density is high. To do.

In the present embodiment, whether or not the noise density of the multipath noise is equal to or higher than a predetermined noise density is
It is determined whether or not the outputs of the two integrating circuits having different time constants have reached a predetermined voltage level. That is, when the noise density is low, only the output of the second integrating circuit 48 having a small time constant is output to the ON voltage V1, and the output from the first integrating circuit 47 having a large time constant does not reach the ON voltage V1. In this case, it is determined that the noise density is low, and the degree of separation is regulated to 10 dB. When the output from the first integrating circuit 47 reaches the on-voltage V1, it is determined that the noise density is high, and the degree of separation is regulated to 4 dB or less.

When reducing noise, it is preferable that the degree of separation is reduced immediately after the detection of multipath noise. The transistors T3 and T4 are circuits for determining whether or not the noise density is equal to or higher than a predetermined density. The time W20 until the output from the first integration circuit 47 turns on the transistor T3 and the on-voltage reaches V1 is
It is longer than the time W12 until the output of the second integration circuit 48 reaches the on-voltage V1. Therefore, when multipath noise occurs, the separation factor is reduced to 10 dB when the time W12 elapses from the time when the noise is detected regardless of the magnitude of the noise density.

Therefore, when the integrator circuits having different time constants are operated in parallel, the integrator circuits having small time constants output the outputs at the levels at which the transistors can be sequentially turned on. Therefore, by operating a plurality of easy circuits such as an integrator circuit in parallel, the attack time from the time when noise is generated until the degree of separation decreases can be defined by the integrator circuit having the smallest time constant. Therefore, the attack time can always be set short.

FIG. 13 shows a stereo receiver 1 according to this embodiment.
3 is a diagram showing the relationship between the S meter voltage and the degree of separation in FIG. When multipath noise is not generated, the S meter voltage and the separability increase as the S meter voltage rises as shown by the solid line 101. That is, when the electric field strength of the received signal is equal to or higher than a predetermined level, the left and right channel audio signals are separated with the maximum separation degree Max. When the S meter voltage becomes less than the predetermined voltage, the degree of separation decreases according to the S meter voltage.

When multipath noise is generated, the degree of separation is a predetermined level shown by solid lines 102 and 103 regardless of the S meter voltage, for example, 4 dB or less shown by solid line 103 when the noise density is higher than the predetermined density. level,
When the noise density is less than the predetermined density, the solid line 102
The separation degree is maintained at about 10 dB.

FIG. 14 is a graph showing the relationship between the degree of separation and the passage of time when the noise density is higher than the predetermined density. As indicated by the solid line 105, when the time W12 elapses after the noise is detected, the separation degree is reduced from the maximum value Max to 10 dB at the time t12.
Next, from time t12 to time t15, further 1
It is reduced from 0 dB to 4 dB. Therefore, the attack time, which is the time after the noise is detected until the separation degree starts to decrease below the maximum value, is always the second time with a small time constant.
It is defined by the output level of the integrating circuit 48.

FIG. 15 is a graph showing the relationship between noise density and release time. As described above, when the degree of separation is reduced from the maximum value Max to 10 dB, the listener does not feel that the stereo feeling is impaired. Therefore, when the separation is reduced to 10 dB, that is, when the noise density does not reach the predetermined density α,
Release time is extremely short. Further, when the noise density is equal to or higher than the predetermined density α, which is set in advance, the degree of separation is reduced to 4 dB. At this time, the listener feels that the stereo broadcasting is switched to the monaural broadcasting, so the release time is set to prevent the sound from being suddenly switched from the monaural broadcasting to the stereo broadcasting and causing a feeling of sound fluctuation. Take a long time of 1 second or more.

As described above, the stereo receiver 1 of the present embodiment
1 defines how much the degree of separation of stereo broadcasting should be reduced according to the presence or absence of multipath noise and the magnitude of the noise density of the multipath noise. Further, the release time for returning the separation degree to the original maximum value is determined according to the level at which the separation degree is lowered.

In the stereo receiver 11 of this embodiment, the degree of separation is lowered in a plurality of steps in response to the noise density. As another embodiment, the separation degree is continuously changed according to the noise density until the noise density reaches a predetermined density α as shown by a solid line 108 in FIG. May be reduced to 4 dB or less. At this time, the degree of separation is 10 from the maximum value Max.
It is gradually and continuously lowered to dB.

When the noise density is lower than the predetermined density α, the degree of separation is preferably reduced to a value between the maximum value Max and the maximum value 10 dB. When the degree of separation is reduced from the maximum value of the degree of separation to 10 dB, the listener does not feel the discomfort that the stereo broadcasting is changed to monaural broadcasting due to the lowering of the degree of separation. Therefore, in this case, even if the degree of separation is rapidly returned to the original maximum degree of separation in a short time, there is no swaying feeling that the stereo broadcast and the monaural broadcast are suddenly switched.

Further, when the noise density is equal to or higher than the predetermined density α, it is preferable to reduce the degree of separation to 4 dB or less which maximizes the noise reducing ability. Further, in this case, the listener feels that the stereo broadcast is close to the monaural broadcast and the audio signals of the opposite channels are mixed with the audio signals of the left and right channels, and the stereo broadcast is in a state close to that of the monaural broadcast. Have been heard. At this time, the degree of separation is gradually increased over time to prevent a stereoscopic sound and a monaural broadcast from being suddenly switched and causing a feeling of sound fluctuation.

As described above, in the stereo receiver of the present embodiment, depending on the presence or absence of multipath noise and the noise density,
Set the amount of separation reduction and release time. Therefore, especially when the noise density is low, the sound reproduced each time noise is generated switches from stereo sound to monaural sound, making the listener feel uncomfortable, and the sound reproduced for a longer time than necessary is monaural sound. Can be prevented from approaching.

Further, in the stereo receiver 11 of this embodiment, the noise density is measured by using a plurality of integrating circuits having different time constants. The degree of separation is set to a value corresponding to the corresponding integrating circuit when the measured integrated output reaches a predetermined level or higher. The noise density measurement is not limited to this method, and other methods may be used. For example, the time constants of the integrating circuits are equal, and a plurality of discriminating levels of the level discriminating means such as the base voltage of the transistor are set to be different. When the output of the integrating circuit exceeds each discrimination level, it may be determined that the noise density corresponding to the level has been reached, and the separation degree control means may set the separation degree corresponding to the level.

[0117]

According to the present invention, in the stereo receiver,
The received signal is received and demodulated, the audio signals of the left and right channels are separated according to the degree of separation, and the audio of each channel is reproduced.
The degree of channel separation is changed according to the electric field strength of the received signal. In addition, when sudden noise is superimposed on the received signal, it is changed according to the noise density of the noise signal regardless of the presence or absence of the electric field strength.

As a result, when the noise density is small and noise is discretely generated, and when the noise density is large and a large number of noises are constantly generated, the degree of separation is set to a value corresponding to each case. Can be set to. Therefore, it is possible to reduce the generated noise in response to the number of times the noise is generated, the generation interval, and the like, and it is possible to separate the audio signal with a degree of separation that can maintain a stereo feeling as much as possible. Therefore, it is possible to prevent the listener from feeling that the stereo sound is frequently switched to the monaural sound.

Further, according to the present invention, when the noise density is equal to or higher than a predetermined density, the separability is reduced to near 0 dB to sufficiently reduce the noise even if the stereo sound approaches the monaural sound. Prioritize. When the noise density is less than the predetermined density and the number of times the noise is generated is small, the separation degree is reduced to about 10 dB to reduce the noise while maintaining the stereo feeling. As a result, it is possible to reduce noise and not lose the sense of stereo when noise is discretely generated and the number of occurrences is small. Therefore, it is possible to reduce noise generated at low density without a feeling of strangeness without changing the sound image or localization of the voice.

Further, according to the present invention, when the resolution is returned to the value before the reduction after reducing the resolution for noise reduction, the value is increased with the passage of time. The release time from the state where the degree of separation is lowered to the original is
As the noise density decreases and the degree of separation in the lowered state increases, the length decreases. The greater the degree of separation in the lowered state, the more the stereo feeling is maintained, and the smaller the change in the sound and localization of the voice when returning.

As a result, even if the sound is restored in a short time, a feeling of strangeness such as switching between stereo sound and monaural sound is reduced. Therefore, the time for which the degree of separation is reduced becomes shorter according to the noise density, and the time for outputting stereo sound becomes longer. Therefore, it is possible to reduce noise and maintain a stereo feeling of reproduced sound.

Further, according to the present invention, the release time of the degree of separation is preferably set to 1 second or more when the degree of separation is lowered until the stereo sound approaches the analog sound as much as possible. When the degree of separation is gradually increased over such a long time, the listener feels that the sound that is as close as possible to the analog sound has returned to the stereo sound without any significant change in the sound image or localization, causing a sense of discomfort. Does not happen. Therefore, even in a state where a lot of noise is generated, the stereo broadcast can be reproduced and listened to satisfactorily.

Further, according to the present invention, the noise density is measured by determining whether or not the outputs from a plurality of integrating circuits having different integration time constants have reached a predetermined discrimination level. The discrimination levels of the level discriminating means for discriminating the level of the integrated output of each integrating circuit are equal. Therefore, a plurality of level discriminating means can be configured by combining a plurality of circuits having the same configuration. Further, in order for the output of the integrating circuit having a large integration time constant to reach the discrimination level, noise having a large noise density is required. Therefore, as the output from the circuit having a larger integration time constant is present, the degree of separation is reduced. Therefore, it is possible to measure the noise density and determine the degree of separation by using a measuring unit having a simple configuration such as an integrating circuit or a transistor. Therefore, the configuration of the noise density measuring means can be simplified.

According to the present invention, the noise density is measured by determining whether or not the output from the integrating circuit is higher than any one of a plurality of predetermined discrimination levels. The integration time constants of the integrating circuits are equal. Therefore, a single integrating circuit can be used, or a plurality of circuits having the same configuration can be combined. Further, in order for the output from the integrating circuit to reach a high discrimination level or higher, noise with a high noise density is required. Therefore, the greater the output from the integrating circuit, the smaller the degree of separation. Therefore, it is possible to measure the noise density and determine the degree of separation by using a measuring unit having a simple configuration such as an integrating circuit or a transistor. Therefore, the configuration of the noise density measuring means can be simplified.

Further, according to the present invention, the mutual relation of the time constants of the plurality of integrating circuits is equal in the case where noise does not exist and the case where noise is extracted. That is, when noise is extracted, the integrated output of the integrator circuit for measuring a small noise density reaches the discrimination level or higher at a timing earlier than the integrated output of the integrator circuit for measuring a large noise density. On the contrary, when noise does not occur, the integrated output of the integration circuit for measuring the small noise density returns to the discrimination level or lower at a timing earlier than the integrated output of the integration circuit for measuring the large noise density.

Further, according to the present invention, each of the level discriminating means outputs signals of one level and the other level to indicate whether the noise density is equal to or higher than or lower than the density determined by the means. When the separation degree control means obtains a signal of one level indicating that the noise density is equal to or higher than the discrimination level of the discrimination means from the plurality of level discrimination means, the separation degree is set corresponding to the discrimination level having the highest density. To do.

As described above, when the degree of separation is set based on the output level of the integrator circuit, one level showing a large noise density is obtained when the integration time constant of the integrator circuit is different and when the discrimination level is different. The output timing of the signal is slow. Therefore, it is determined that the value of the noise density of the received signal satisfies the preset discrimination level, from the low discrimination level among a large number of discrimination levels, and the signal is output. Therefore, the attack time from the occurrence of noise to the start of the decrease in separation is always determined based on the output of the integrating circuit having a low discrimination level. Therefore, in the circuit having the simple structure described above, the attack time can always be made constant. Therefore, when multipath noise occurs, it is possible to always start decreasing the degree of separation in a short time.

[Brief description of drawings]

FIG. 1 is a stereo receiver 1 according to an embodiment of the present invention.
2 is a block diagram showing an electrical configuration of 1. FIG.

FIG. 2 is a circuit diagram showing a specific configuration of an S meter circuit 32.

3 is a waveform diagram showing an output signal from an intermediate frequency amplifier circuit 20 given to an S meter circuit 32. FIG.

4 is a diagram showing the relationship between the electric field strength of the output signal given from the intermediate frequency amplifier circuit 20 and the S meter voltage outputted from the S meter circuit 32. FIG.

5 is a circuit diagram showing a specific configuration of a multipath detection circuit 42. FIG.

FIG. 6 is a circuit diagram showing a specific configuration of integrating circuits 47 and 48 and waveform shaping transistors T3 and T4.

7 is a block diagram showing a specific configuration of the channel separation circuit 22. FIG.

FIG. 8 is a coefficient k1 determined by coefficient multiplication circuits 68 and 72.
5 is a graph showing the relationship between the control voltage and the control voltage.

FIG. 9 shows a multipath detection circuit 42 to a separation degree control circuit 3
4 is a waveform diagram showing the output of each circuit up to 4.

FIG. 10 is a graph showing the relationship between the noise generation timing and the change in the degree of separation when the noise density is small.

FIG. 11 is a graph showing the relationship between the noise generation timing and the change in the degree of separation when the noise density is medium.

FIG. 12 is a graph showing the relationship between the noise generation timing and the change in the degree of separation when the noise density is high.

FIG. 13 is a diagram showing the relationship between the S meter voltage and the degree of separation.

FIG. 14 is a graph showing the relationship between the degree of separation and the passage of time when the noise density is higher than a predetermined density.

FIG. 15 is a graph showing the relationship between noise density and release time.

FIG. 16 is a graph showing the relationship between noise density and separation degree.

FIG. 17 is a graph showing the relationship between the noise generation timing and the change in the degree of separation when the noise density is low in the conventional stereo receiver.

FIG. 18 is a graph showing the relationship between the noise generation timing and the change in the degree of separation when the noise density of the conventional stereo receiver is medium.

FIG. 19 is a graph showing the relationship between the noise generation timing and the change in the degree of separation when the noise density is large in the conventional stereo receiver.

[Explanation of symbols]

 11 stereo receiver 12 antenna 13 tuning circuit 14 high frequency amplification circuit 15 mixing circuit 16 local oscillator 17 PLL 18 control circuit 19 narrow band filter 20 intermediate frequency amplification circuit 21 frequency discrimination circuit 22 channel separation circuit 23 tone control circuit 24 amplification circuit 25 speaker 32 S meter circuit 34 Separation control circuit 42 Multipath detection circuit 47 First integration circuit 48 Second integration circuit T3, T4 Transistors D6, D7 Diodes R15, R16, R17, R18 Resistance G10 Capacitor 68, 72 Coefficient multiplication circuit

Claims (8)

[Claims] 1. A receiving means for receiving a received signal, a demodulating means for demodulating the received signal in response to an output of the receiving means, and an output of the demodulating means is operated based on a separability control signal to control the separability. A channel separation unit that separates and derives the demodulated received signal into audio signals for each of the left and right channels with a degree of separation that corresponds to the signal level, and detects the electric field strength of the received signal in response to the output of the receiving unit. , A field intensity detection means for outputting a separation control signal for controlling the channel separation means so as to reduce the separation degree as the electric field strength decreases, and a noise extraction for extracting a noise signal from the reception signal in response to the output of the reception means. Means, in response to the output of the noise extraction means, the noise density measuring means for measuring the noise density, and in response to the output of the noise density measuring means, the higher the noise density, a plurality of steps or continuously, A separation degree control means for outputting a separation degree control signal for controlling the channel separation means so as to set the separation degree small, and a separation degree control output from the electric field strength detection means when noise is not extracted by the noise extraction means. A stereo receiver, comprising: a switching means for supplying a signal to the channel separation means and, when noise is extracted, for supplying the channel separation means with the separation control signal output from the separation control means. 2. The channel separating means extracts a noise signal, and when the noise density is equal to or higher than a predetermined density, sets the degree of separation below a predetermined value, extracts the noise signal, and extracts the noise density. When the density is less than a predetermined density, the degree of separation is set to about 10 dB, and the predetermined value is set to a value that can sufficiently reduce noise. Receiving machine. 3. The separation control means controls the channel separation means so as to reduce the separation, and thereafter, when a noise signal is not extracted from the received signal, the separation control increases the separation with time and returns. 3. The stereo receiver according to claim 2, wherein the time change rate of the degree of separation controlled by the above-mentioned control and increased with time is set smaller as the noise density becomes smaller. 4. When the noise density is equal to or higher than the predetermined density, the temporal change rate of the separation degree is determined in accordance with the electric field strength of the received signal, the separation degree set to less than the predetermined value. The stereo receiver according to claim 3, wherein a release time required for returning to the separation degree is set to be about 1 second or more. 5. The noise density measuring means discriminates a plurality of integrating circuits having different integration time constants for charging or discharging the noise from the noise extracting means from each other, and the integrated output of each integrating circuit is individually discriminated from each other. , And a plurality of level discriminating circuits having the same discriminating level, wherein the separation degree control means responds to the output of each level discriminating means and outputs the level discriminating means corresponding to the integrating circuit having a large integral time constant. The channel separating means is controlled so that the separation degree becomes smaller when the output of the level discriminating means corresponding to the integrating circuit having a smaller integration time constant is obtained when is obtained. Stereo receiver according to 1. 6. The discharging or charging time constant of each of the integrating circuits in the absence of noise is selected to be larger as the charging or discharging time constant when noise is extracted is larger. Stereo receiver. 7. The noise density measuring means discriminates a level individually from a plurality of integrating circuits having the same integral time constant for charging or discharging the noise from the noise extracting means, and the integrated output of each integrating circuit. , And a plurality of level discrimination circuits whose discrimination levels are different from each other, wherein the separation degree control means is responsive to the output of each level discrimination means, and when the output of the level discrimination means having a large discrimination level is obtained, 2. The stereo receiver according to claim 1, wherein the channel separating means is controlled so that the degree of separation is smaller than when the output of the level discriminating means having a small discriminating level is obtained. 8. The level discriminating means responds to the output of the integrating circuit, outputs a signal of one level when the discriminating level is above a predetermined discriminating level, and outputs a signal of the other level when the discriminating level is below the predetermined discriminating level. The separation degree control means has a switching means for outputting, and when one level signal is obtained from each level discrimination means, the separation degree control means discriminates the degree of separation among the level discrimination means outputting one level signal. 8. The stereo receiver according to claim 5, wherein the channel separating means is controlled so that the level or the corresponding integrating time constant of the integrating circuit becomes a value corresponding to the level discriminating means.